c - 提供下面提到的 typedef 和 #define 行为差异的原因

Question

我已经浏览了可用的现有信息

difference between typedef and define & typedef,#define

所有回复都非常有用。我刚遇到一个例子，任何人都可以提供这种行为的原因。

对于声明 unsigned int 变量，这将起作用:

#define INTEGER int
unsigned INTEGER i = 10;

但是，它在 typedef 的情况下不起作用，

例如

typedef int INTEGER;
unsigned INTEGER i = 10;

它会抛出错误:'i' undeclared (first use in this function)

提前致谢!

Answer 1

预处理器只是进行复制和粘贴。当你写:

#define INTEGER int
unsigned INTEGER i = 10;

在编译器本身之前，预处理器将代码放入:

unsigned int i = 10;

然而，typedef由编译器处理。

C11 (n1570), § 6.7.8 Type definitions

A typedef declaration does not introduce a new type, only a synonym for the type so specified. That is, in the following declarations:

typedef T type_ident;
type_ident D;

type_ident is defined as a typedef name with the type specified by the declaration specifiers in T (known as T), and the identifier in D has the type ‘‘derived-declarator- type-list T ’’ where the derived-declarator-type-list is specified by the declarators of D.

换句话说，<INTEGER>是 <int> 的同义词.但是<unsigned INTEGER>被视为不存在的单一类型。